Augmentation

ABSTRACT

A method of anchoring an implant in hard tissue, and/or hard tissue replacement material, includes the steps of providing an initial opening in the hard tissue, providing a thermoplastic augmentation element, a tool and a counter element, compressing the augmentation element between the tool and the counter element while energy is coupled into the tool and while a periphery of a liquefaction interface of the tool and the augmentation element and/or of a liquefaction interface of the augmentation element and the counter element is in the opening, thereby liquefying material of the augmentation element at the liquefaction interface(s) to yield liquefied material, causing portions of the liquefied material to penetrate into structures of the hard tissue, allowing the liquefied material to harden and to thereby become augmentation material, removing the tool and the counter element, and anchoring the implant in the opening including at least some of the augmentation material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is in the field of anchoring objects in hard tissue and/orhard tissue replacement material, such as bone. Especially, it is suitedfor anchoring objects in weak or brittle hard tissue, such asosteoporotic bone.

2. Description of Related Art

If screws are anchored in live bone tissue, often the problem ofinsufficient bone stability or insufficient stability of the anchoringin the bone arises. Especially, in trabecular bone tissue, any loadacting on the screw is passed over to only few trabeculae, with adverseconsequences both for the load bearing capability of the screw-boneconnection and for its long-time stability. This is especially severe inosteoporotic or otherwise weakened bone tissue.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide methods and devicesfor anchoring implants overcoming disadvantages of prior art implantanchoring methods.

According to a first aspect of the invention, a method of anchoring animplant in hard tissue and/or hard tissue replacement material isprovided, the method comprising the steps of providing an initialopening in the hard tissue and/or hard tissue replacement material, ofproviding a thermoplastic augmentation element, a tool and a counterelement, of compressing the augmentation element between the tool andthe counter element while energy is coupled into the tool and/or theaugmentation element and while a periphery of a liquefaction interfaceof the oscillation tool and the augmentation element and/or of aliquefaction interface of the augmentation element and the counterelement is in the opening, thereby liquefying material of theaugmentation element at the liquefaction interface(s) to yield liquefiedmaterial, causing portions of the liquefied material to penetrate intostructures of the hard tissue and/or hard tissue replacement material orconnected thereto, allowing the liquefied material to harden and tothereby become augmentation material, removing the oscillation tool andthe counter element, and anchoring the implant in the opening comprisingat least some of the augmentation material.

The tool may be an oscillation tool, and the step of coupling energyinto the tool and/or the augmentation element may then comprise couplingmechanical oscillations into the oscillation tool. The material iscaused to liquefy at the interface due to external and/or internalfriction.

As an alternative, the tool may be caused to rotate, whereby the energycoupled into the system is rotational mechanical energy, the materialbeing caused to liquefy at the interface due to friction.

As yet another alternative, electromagnetic radiation may be coupled,for example, by the tool into the augmentation element (which then isessentially transparent for the electromagnetic radiation at the usedwavelength), and may be absorbed at the interface so that the heatarising therefrom causes the liquefaction.

As an even further alternative, the tool may be a heater provided with aheater, whereby the energy coupled into the system is heat.

The structures may be structures of a circumferential wall of theopening if the opening is a bore-like structure. For example, if thehard tissue and/or hard tissue replacement material comprises cancellousbone, the structures may include the structures of trabeculae withspaces between them. If the hard tissue and/or hard tissue replacementmaterial comprises cortical bone, the structures may include structuresof the cortical bone. If the if the hard tissue and/or hard tissuereplacement material is a porous bone replacement material—such as ametallic foam or a hydraulic cement or a autograft or allograft bone,the structures comprise pores or other structures of such bonereplacement material. In this, the opening may also be an opening with acircumferential wall that does not surround the interface without anyinterruption, but that for example is a gap of a joint.

Alternatively, the structures may be structures of a device connected tothe hard tissue and/or hard tissue replacement material. For example,pedicle screws for spine stabilization devices have become known, whichpedicle screws comprise a radially expandable segment or element. Theexpandable segment or element expands within the cancellous bone duringthe surgical implantation and creates a channel with a porous wall thatallows interdigitation for example by cement. The approach describedherein allows filling of the channel and the porous wall of theelement/segment by thermoplastic material from within the device.

The interface between the tool and the augmentation element (and/or, asthe case may be, between tool and counter element) where liquefyingtakes place defines a liquefaction interface (or, if liquefaction takesplace at the two interfaces, define two liquefaction interfaces).Usually and preferably, the interface between the tool and theaugmentation element is the liquefaction interface.

In case the energy coupled into the system is oscillation energy, thesystem may as an alternative be designed so that the liquefactioninterface is the interface between the counter element and theaugmentation element (solely or in addition to the interface between thetool and the augmentation element). To this end, the augmentationelement comprises special shape—for example it may be substantiallythinner at the interface to the counter element, so that theoscillations may be transmitted through the augmentation element towardsthe counter element, and also the interface between the counter elementand the augmentation element may be the liquefaction interface.

Also in case the energy coupled into the system is rotational energy, itis possible to cause the liquefaction interface to be the interfacebetween the counter element and the augmentation element, for example bycoupling the augmentation element to the rotation tool so that therotational mechanical movement is coupled into the augmentation elementas well and the friction arises at the interface between the counterelement and the augmentation element.

Finally, if the energy is radiation energy or heat, the interface(s) atwhich liquefaction takes place may be chosen in accordance with theparticular needs.

In the following text, the expression “augmentation process” refers tothe sub-sequence of the following steps:

-   -   placing the augmentation element, the tool and the counter        element so that a periphery of the liquefaction interface(s)        is/are adjacent the circumferential wall,    -   compressing the augmentation element between the tool and the        counter element energy is coupled into the oscillation tool and        while a periphery of the liquefaction interface(s) is in the        opening, thereby liquefying material of the augmentation element        to yield liquefied material,    -   causing portions of the liquefied material to penetrate into        structures of the hard tissue and/or hard tissue replacement        material or device connected thereto,    -   allowing the liquefied material to harden and to thereby become        augmentation material, and    -   removing the tool and the counter element.

It is an aspect of the invention to provide the concept of anaugmentation process of hard tissue with the aim of anchoring an otherobject by means of mechanical oscillations, for example ultrasonicvibrations.

The steps of allowing the liquefied material to harden and of removingthe tool and the counter element may be carried out one after the otherin arbitrary sequence, or may be carried out simultaneously. Often, theaugmentation material is caused to augment an extended part of thecircumferential surface, i.e. has a substantial axial extension. Then,the augmentation process includes moving the liquefaction interface(s)or at least one liquefaction interface in an axial direction while theenergy impinges (i.e. for example while the oscillations act). In such asituation, the hardening in one region may have taken place while inanother region, at an axial distance from the one region, theliquefaction may still take place.

The augmentation process can be repeated several times, so that over thelength of the opening several desired spots are augmented. As anexample, for a pedicle screw, an augmentation may be carried outdistally within the vertebral body, medially in the region of thepedicle, and maybe even proximally for the enforcement of the proximallamina.

From the liquefaction interface, during the liquefaction step, theliquefied material flows usually radially outward into the structures ofthe hard tissue and/or hard tissue replacement material (or, as the casemay be, of the device connected thereto). Thus, a periphery of theliquefaction interface forms a part of the peripheral interface of thetool—augmentation-element—counter-element assembly. The structures ofthe hard tissue and/or hard tissue replacement material may be a porousstructure made up of spaces between trabeculae or similar. They may alsobe artificially added or naturally occurring roughnesses or the like.Almost any structure that deviates from an even surface is suitable,however, structures with ‘undercut’ like features are preferable.

A first special class of hard tissue/hard tissue replacement materialsuitable to be augmented by the method according to the invention istrabecular bone, for example osteopenic or osteoporotic bone. A secondspecial class of hard tissue/hard tissue replacement material where theinvention is especially useful is spongy bone substitute material suchas autograft or allograft bone tissue (including cadaver bone material),trabecular metal (especially titanium foam or tantalum foam), orhydraulic cement such as used for vertebroplasty. The approach accordingto the invention thus allows to use, as hard tissue replacementmaterial, spongy, porous material that is highly suitable for ingrowthof real bone material, and to nevertheless soundly anchor the implant init.

Even though the opening in the hard tissue and/or hard tissuereplacement material may be a blind hole, a gap (of a joint or the like)or a through opening, the removal of both, the tool and the counterelement in many embodiments has to take place to one and the same side,namely to the proximal side. This implies that in these embodiments theaugmentation material will leave a final opening through which thedistal portion of the tool or the counter element is pulled during theaugmentation process. The cross sectional area of the final openingwill, thus, at least be equal to the cross sectional area of the mostdistal portion of the oscillation tool or the counter element,respectively. This distal portion, however, is the portion that servesfor compressing the augmentation element during the liquefaction of thethermoplastic material. Thus, during the augmentation process, the wholeaugmentation element (or at least a whole axial section of it) has to becompletely displaced outwardly from its initial position. If theaugmentation element is tube shaped or has the shape of a plurality ofconnected or unconnected tube sectors, an inner diameter of the finalopening will thus be greater than an average diameter of theaugmentation element before the augmentation process. In other words,according to a further aspect, the augmentation material during theaugmentation process is displaced from an initial, inner position to afinal, outer position, by at least a radial distance that corresponds tohalf a wall thickness of the tube wall of the augmentation element.

According to a preferable version, an inner diameter of the augmentationmaterial remaining anchored in the hard tissue and/or hard tissuereplacement material after the augmentation process may even be largerthan an outer diameter of the augmentation element prior to theaugmentation process. Thus the tool—or potentially the counterelement—is moved, during the augmentation process throughthe—entire—space where the augmentation element was placed at the onsetof the liquefaction step.

Also, preferably, during liquefaction an entire cross section of theaugmentation element is liquefied. The liquefaction interface to thispurpose covers, in a projection along a movement axis that may also bean opening axis, an entire cross section of the augmentation element.The liquefaction step therefore includes continuously melting away, atthe liquefaction interface an entire cross section of the augmentationelement and displacing it outwardly into and onto the structures of theopening, while the liquefaction interface moves with respect to thecounter element (and/or to the tool) and to the body of the remainingaugmentation element to continuously ‘eat away’ the remainingaugmentation element. The process may, according to a preferablevariant, be continued until the tool contact surface and the counterelement contact surface contact each other, so that the augmentationelement is fully displaced (‘used up’). However, it is also possible tostop the process and to remove remaining augmentation element portionstogether with and between the tool and the counter element.

In many embodiments where the liquefaction interface is the interfacebetween the tool and the augmentation element, not only the liquefactioninterface is subject to an axial movement, but also the interfacebetween the augmentation element and the counter element. Then, anoverall length of the augmentation material is shorter than an initiallength of the augmentation element.

There are two basic configurations of the method and device according tothe invention. In a first, preferred configuration, the tool contactsurface is at a distal end of the augmentation element, and the forcefor compressing the augmentation element is coupled into the tool as atensile force—the tool is pulled. To that effect, the tool may comprisea shaft portion and a distal broadening, a rearward (i.e. towards theproximal side) facing surface forming the tool contact surface. Thecounter element then is a “pusher” that may be moved forward (towardsthe distal side) during the liquefaction step, or that may be heldstill, depending on how much augmentation material per axial length unitis to be disposed. The counter element may, for example, be of a rigidmaterial with a tube shaped end forming the counter element contactsurface. It is in any case preferred if the counter element canoptionally be pushed forward and into the opening during the process.If, however, the counter element is not to be moved forward, it may alsohave the shape of a plate to be held against the hard tissue and/or hardtissue replacement material surface, or similar.

This “retro” configuration features the advantage of providing maximumflexibility while keeping the contact surfaces between the tool and thesensitive tissue surface at a minimum.

In a second, “forward” configuration, the tool contact surface is at aproximal end of the augmentation element, and the force for compressingthe augmentation element is coupled into the tool as a pressingforce—the tool is pushed. Then, it is the counter element that reachesto the distal side and may comprise a shaft portion and a distalbroadening with a rearward facing surface forming the counter elementcontact surface.

In the “retro” configuration, the tool may, in addition to theaugmentation process, serve a different purpose. During insertion, in afirst, forward movement the tool may also be used for creating orexpanding the opening in the hard tissue/hard tissue replacementmaterial by means of a cutter and/or chisel like function by having, ona distal side, appropriate shapes. Such cutter and/or chisel likefunctions are as such known from ultrasound processing/machining of boneand tooth material. By this measure, a process step can be saved, andalso holes can be created and augmented that do not have a circularcross section.

In any configuration, the augmentation element may comprise an axiallythrough-going, for example central, opening for the tool (for the retroconfiguration) or for the counter element (for the forwardconfiguration). The axis of the central opening which is preferablyparallel to the movement axis and to the opening axis. The augmentationelement may for example be essentially tube shaped or comprise one or aplurality of sections (sectors) covering different angle ranges (thesectors, by their arrangement defining the central opening). It may,however, also be configured differently and, for example, comprisehelical structures or the like.

The implant may be a fastening device for fastening other objects to thetissue or for fastening tissue parts to each other. The implant as analternative may also serve as any kind of prosthesis.

For implantation of the implant in the augmented opening, anchoringstructures of the implant are brought in intimate contact with thethermoplastic augmentation material. The intimate contact may be such asto cause a mechanical anchoring, such as a positive-fit anchoring,and/or such as to cause an anchoring by bonding.

The implant to be anchored in the opening may therefore, according to afirst embodiment of the invention comprise fastening and/or retentionstructures for a mechanical connection (mechanical anchoring), forexample by a positive fit connection. Examples of such fastening and/orretention structures are a thread, a barbed structure, rivet-kindstructures etc. These structures are preferably such as to engage intothe augmented hard tissue and/or hard tissue replacement material, i.e.with reference to a hole axis of the initial hole, they reach furtherout than the hole radius. As a second embodiment, in addition or as analternative, the implant to be implanted may comprise surface materialportions that may be bonded (positively bonded, substance-to-substancebonded; adhesive bonded) to the augmentation material, for example bywelding.

If formed according to the first embodiment, the implant may comprise athreaded section and act as screw. The thread of the screw then engagesinto the hard tissue and/or hard tissue replacement material augmentedby the augmentation material. The screw diameter in this situation ischosen so that an outer diameter of the threaded section is greater thana diameter of the initial opening.

Depending on the size of the threaded section and on parameters of itsthread—such as the thread pitch and the thread height, the augmentedhard tissue and/or hard tissue replacement material may produce asubstantial resistance against introduction of the threaded section. Ifthis is the case, in the augmentation process according to theinvention, the tool (and/or potentially the counter element) maycomprise structures for conditioning the augmentation material to easeintroduction of a thread. For example, the tool may comprise radiallyprotruding blades confining the flow of the liquefied thermoplasticmaterial to certain azimuthal angles. Thereby the augmentation materialobtains a slitted structure that offers less resistance to radialexpansion by an element introduced into the opening. As an alternative,the tool may comprise a rotatably mounted thread cutting section todirectly cut a thread during the augmentation process.

If formed according to the second embodiment, the implant may be formedas for example described in WO 02/069 817, WO 2004/017 857, WO 2005/079696, WO 2008/034 277, or U.S. provisional patent application 60/983,791,the teaching of all of these references being incorporated herein byreference. All these references teach to liquefy thermoplastic materialby mechanical oscillations and to cause liquefied thermoplastic materialto penetrate into porous structures of the tissue they are to beanchored in. When used in combination with the approach according to theinvention, however, the thermoplastic material of the implant will atleast partially be welded together with the augmentation material,instead of or in addition to forming a positive-fit connection. If,according to the second embodiment, a bond is formed between theaugmentation material and material of the implant, welding by means ofapplying mechanical oscillations to the implant is preferred, becausethen the thermoplastic material is melted only locally at surfaceportions, for example at the places of energy directors. By thismeasure, the overall heat impact is substantially lower, and the use ofthermoplastic materials with melting temperatures substantially above37° C. is readily possible. Nevertheless, the invention does not excludethe welding by other means, such as by thermal heating, especially ifthe implant is very small, at places where the heat impact does notproduce extensive damages and/or if the melting temperature of thethermoplastic augmentation materials and/or the thermoplastic implantmaterial is not far above 37° C.

The thermoplastic material of the augmentation element may behomogeneous or made up of different components (such as of an inner andan outer layer of different hardness). The thermoplastic material may benon-resorbable or may be at least partly resorbable. If the primarystability provided by the augmentation material is to be retained, thethermoplastic material is not resorbable or only partly resorbable.

Suitable Resorbable polymers are e.g. based on lactic acid and/orglycolic acid (PLA, PLLA, PGA, PLGA etc.) or polyhydroxyalkanoates(PHA), polycaprolactones (PCL), polysaccharides, polydioxanones (PD),polyanhydrides, polypeptides or corresponding copolymers or blendedpolymers or composite materials containing the mentioned polymers ascomponents are suitable as resorbable liquefiable materials.Thermoplastics such as for example polyolefins, polyacrylates,polymetacrylates, polycarbonates, polyamides, polyesters, polyurethanes,polysulphones, polyaryl ketones, polyimides, polyphenyl sulphides orliquid crystal polymers (LCPS), polyacetals, halogenated polymers, inparticular halogenated polyoelefins, polyphenylene sulphides,polysulphones, polyethers, polypropylene (PP), or correspondingcopolymers or blended polymers or composite materials containing thementioned polymers as components are suitable as non-resorbablepolymers.

Specific embodiments of degradable materials are Polylactides like LR706PLDLLA 70/30, R208 PLDLA 50/50, L210S, and PLLA 100% L, all ofBöhringer. A list of suitable degradable polymer materials can also befound in: Erich Wintermantel und Suk-Woo Haa, “Medizinaltechnik mitbiokompatiblen Materialien und Verfahren”, 3. Auflage, Springer, Berlin2002 (in the following referred to as “Wintermantel”), page 200; forinformation on PGA and PLA see pages 202 ff., on PCL see page 207, onPHB/PHV copolymers page 206; on polydioxanone PDS page 209. Discussionof a further bioresorbable material can for example be found in C ABailey et al., J Hand Surg [Br] 2006 April; 31(2):208-12.

Specific embodiments of non-degradable materials are: Polyetherketone(PEEK Optima, Grades 450 and 150, Invibio Ltd), Polyetherimide,Polyamide 12, Polyamide 11, Polyamide 6, Polyamide 66, Polycarbonate,Polymethylmethacrylate, Polyoxymethylene. An overview table of polymersand applications is listed in Wintermantel, page 150; specific examplescan be found in Wintermantel page 161 ff. (PE, Hostalen Gur 812, HöchstAG), pages 164 ff. (PET) 169 ff. (PA, namely PA 6 and PA 66), 171 ff.(PTFE), 173 ff. (PMMA), 180 (PUR, see table), 186 ff. (PEEK), 189 ff.(PSU), 191 ff (POM—Polyacetal, tradenames Delrin, Tenac, has also beenused in endoprostheses by Protec).

Examples of suited thermoplastic material include polylactides such asany one of the products LR708 (amorphous Poly-L-DL lactide 70/30), L209or L210S by Böhringer Ingelheim or polycarbonates.

The liquefiable material having thermoplastic properties may containforeign phases or compounds serving further functions. In particular,the thermoplastic material may be strengthened by admixed fillers, forexample particulate fillers that may have a therapeutic or other desiredeffect. The thermoplastic material may also contain components whichexpand or dissolve (create pores) in situ (e.g. polyesters,polysaccharides, hydrogels, sodium phosphates) or compounds to bereleased in situ and having a therapeutic effect, e.g. promotion ofhealing and regeneration (e.g. growth factors, antibiotics, inflammationinhibitors or buffers such as sodium phosphate or calcium carbonateagainst adverse effects of acidic decomposition). If the thermoplasticmaterial is resorbable, release of such compounds is delayed.

Fillers used may include degradable, osseostimulative fillers to be usedin degradable polymers, including: β-Tricalciumphosphate (TCP),Hydroxyapatite (HA, <90% crystallinity; or mixtures of TCP, HA, DHCP,Bioglasses (see Wintermantel). Osseo-integration stimulating fillersthat are only partially or hardly degradable, for non degradablepolymers include: Bioglasses, Hydroxyapatite (>90% cristallinity),HAPEX®, see S M Rea et al., J Mater Sci Mater Med. 2004 September;15(9):997-1005; for hydroxyapatite see also L. Fang et al., Biomaterials2006 July; 27(20):3701-7, M. Huang et al., J Mater Sci Mater Med 2003July; 14(7):655-60, and W. Bonfield and E. Tanner, Materials World 1997January; 5 no. 1:18-20. Embodiments of bioactive fillers and theirdiscussion can for example be found in X. Huang and X. Miao, J BiomaterApp. 2007 April; 21(4):351-74), JA Juhasz et al. Biomaterials, 2004March; 25(6):949-55. Particulate filler types include: coarse type: 5-20μm (contents, preferentially 10-25% by volume), sub-micron (nanofillersas from precipitation, preferentially plate like aspect ratio >10, 10-50nm, contents 0.5 to 5% by volume).

More generally liquefaction is achieved by using materials withthermoplastic properties having a melting temperature of up to about350° C. In embodiments in which the energy is a mechanical oscillationenergy and the tool is an oscillation tool, if the liquefactioninterface or one of the liquefaction interfaces is between theaugmentation element and the counter element, the modulus of elasticityshould be at least 0.5 GPa so that the thermoplastic material transmitsthe mechanical oscillation with such little damping that innerliquefaction and thus destabilization of the augmentation element doesnot occur, i.e. liquefaction occurs only where the liquefiable materialis at the liquefaction interface. If only the interface to theoscillation tool serves as the liquefaction interface, the material mayin principle also have a lower modulus of elasticity. However, due tothe load bearing function the material has, also in this situation amodulus of elasticity should of at least 0.5 GPa is preferred.

The mechanical oscillations applied have of a frequency preferably inthe rage of between 2 and 200 kHz (preferably ultrasonic vibration).

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the invention are described inconnection with the following figures, wherein same reference numeralsrefer to same or equivalent elements. Therein:

FIG. 1 depicts a first embodiment of a device and a method according tothe invention;

FIG. 2 shows a second embodiment of a device and a method according tothe invention;

FIG. 3 schematically illustrates implantation of an implant in anopening in bone tissue augmented by a method according to the invention;

FIG. 4 illustrates implantation of a different implant;

FIG. 5 depicts a further embodiment of a device and a method accordingto the invention;

FIG. 6 shows yet another embodiment of a device and a method accordingto the invention;

FIG. 7 shows an even further embodiment, with a forward movement of theoscillation tool; and

FIG. 8 illustrates the principle of a device where the augmentationelement that is not all around, i.e. that does not cover the entireperiphery.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device shown in FIG. 1 is illustrated partly inserted in an openingin bone tissue 1. The opening preferably is translation symmetrical withrespect to translations parallel to an axis 2, but may have any crosssection perpendicular to that axis. For many embodiments, though, theopening has the shape of a circular cylinder, i.e. the cross section iscircular. The opening 1.1 may have been added to the bone tissue by aconventional method, such as by drilling.

The device parts, as far as to be inserted in the opening 1.1, arerotational symmetric if the opening is circular in cross section. Theycomprise an oscillation tool 3, an augmentation element 4, and a counterelement 5. The augmentation element 4 is formed as a tube of a suitablethermoplastic material.

The oscillation tool 3 may be metallic and comprises a tool shaft 3.1reaching through the augmentation element 4 from a proximal side to adistal side. At the proximal side, the oscillation tool comprises means(not illustrated) for the tool to be coupled to an oscillationgenerator, such as an ultrasonic device. The means are such that atensile force may be coupled into the oscillation tool. At the distalside, the tool comprises a distal broadening 3.2 joined to the shaft3.1. The distal broadening has the shape of a wedge tapering from thedistal to the proximal side where it is attached to the shaft.

The backward-facing surface 3.3 (i.e. the tapering surface facingtowards the proximal side) of the distal broadening 3.2 serves as anoscillation tool contact surface and oscillation tool coupling-outsurface when in contact with a distal first contact surface 4.1 of theaugmentation element. Together, the oscillation tool contact surface 3.3and the augmentation element first contact surface 4.1 form theliquefaction interface.

The proximal end surface of the augmentation element forms the secondaugmentation element contact surface 4.2 against which the counterelement contact surface 5.1 can be pressed during augmentation.

The counter element 5 is tube shaped with a wall thickness preferablyequal to or greater than the wall shape of the augmentation element. Thecounter element may be metallic or of a suitable plastic or ceramicmaterial.

During the augmentation process, mechanical oscillations and a tensileforce are coupled into the oscillation tool 3, while the counter elementis held against the tensile force by a pushing force. Due to the effectof the mechanical oscillations, the thermoplastic material melts at theliquefaction interface. While liquefaction progressively continues atthe liquefaction interface, the oscillation tool is pulled towards theproximal side, and/or the counter element is pushed towards the distalside, so that the length of the remaining, not yet molten augmentationelement portion gradually decreases. Due to the wedge shape of thedistal broadening and due to the lack of other space to go to, themelted augmentation material is pushed sideways into the structures suchas openings, and/or pores of the bone material around thecircumferential wall of the opening 1.1. Thereby the augmentationmaterial forms an augmentation zone 6 in the bone tissue around theopening where the bone material is interpenetrated by the again hardenedthermoplastic augmentation material. The cross section of the remainingfinal opening may, depending on the cross section of the distalbroadening of the oscillation tool, be approximately equal to the crosssection of the initial opening, or slightly less than that. The length(measured along the axis 2) of the augmentation zone 6 may beapproximately equal as the initial length of the augmentation element 4,or it may be less than that, depending on whether the counter element 5is held still during the augmentation process (then the length will beequal) or whether the counter element is pushed forward during theaugmentation process (then the length will be smaller, and the materialin the augmentation zone 6 per length unit will be greater than theinitial material per length unit of the augmentation element.

FIG. 2 depicts a variant of the device and method of FIG. 1. As a firstdifference, the distal broadening on the rearward side comprises a face(forming the oscillation tool contact surface) that tapers inward, i.e.that defines a concave structure. The inclination with respect to anaxis normal plane may for example be between 10° and 60°, especiallyaround 45°. Such inward tapering has been found to be especiallyadvantageous in terms of melting properties: it prevents theaugmentation element from merely being softened, pushed outward and putover the distal broadening without being properly liquefied. Rather, itcenters the augmentation element with respect to the oscillation tooland ensures thorough liquefaction at the liquefaction interface.

The device as depicted in FIG. 2 can be used like the one of FIG. 1 andbe pulled through the opening 1.1 to leave an axially extendedaugmentation zone of desired length, as discussed above.

The configuration depicted difference in FIG. 2, shows, as seconddifference to FIG. 1, the concept of reduced length of the augmentationzone 6 being taken to an extreme: the oscillation tool is held stillduring the augmentation process, so that the entire axial movement inthe augmentation process stems from the forward movement of the counterelement 5. This results in a ring-shaped (instead of tube-shaped)augmentation zone 6.

A set-up as the one illustrated in FIG. 1 or 2 may also be used if theenergy is coupled into the system by way of rotation of the tool 3. Inthis, preferably there is a rotational coupling between the augmentationelement 4 and the counter element 5. For example, the augmentationelement may stick to the surface of the counter element, and/or theaugmentation element and the counter element may compriseinterdigitating structures. Friction then causes the augmentationelement to melt at the interface between the augmentation element 4 andthe tool 3. If, in contrast, the augmentation element is rotationallycoupled to the tool and decoupled from the counter element, theliquefaction will take place at the interface between the augmentationelement and the counter element.

FIG. 3 illustrates the anchoring of an implant 11 in the opening 1.1augmented by the augmentation zone 6. The major diameter of the threadedsection 11.1 of the screw is greater than the diameter of the initialopening 1.1 so that the thread engages into the bone material in theregion of the augmentation zone. The augmentation material of theaugmentation zone helps to distribute the mechanical load in the bonematerial and prevents single trabeculae from being loaded too heavily.

FIG. 4 depicts an alternative embodiment that, in contrast to theembodiment of FIG. 3, is also suitable for openings 1.1 withnon-circular cross sections. The implant 11 comprises a surface orsurface regions of thermoplastic material 13. The implant may, forexample, consist entirely of the thermoplastic material or may be, asdepicted, a hybrid implant with a, for example, metallic or ceramic coreand thermoplastic surface portions. If the implant is a hybrid implant,the thermoplastic surface portions may entirely cover a circumferentialsurface of an anchoring portion 11.3 to be anchored in the bone tissueor only portions thereof, as for example taught in embodiments ofWO2004/017857, the content of which is incorporated herein by reference.The implant 11 further comprises a coupling-in surface 11.5 suitable fora sonotrode to engage to couple mechanical oscillations into theimplant. For implantation, the implant is pushed into the opening atleast to a certain extent, and then mechanical oscillations are coupledinto it, while the implant may optionally be further pushed into theopening. Due to the effect of the mechanical oscillations and thefrictional forces created at the periphery of the anchoring portion11.3, the thermoplastic material 13 starts melting and welds to theaugmentation material of the augmentation zone. Optionally, in additionportions 13 of the thermoplastic material may be pushed into structuresof the bone material so that an additional anchoring of the kind taughtin WO02/069817, also incorporated herein by reference, is achieved.

The thermoplastic material 13 of the implant 11 of FIG. 4 does not needto surround the implant shaft. Also, the cross section of the implantneed not be circular, also in cases where the opening is circular (andthe implant then may comprise self-reaming structures). For example, ifthe cross section is a double-T-shape the thermoplastic material may inan embodiment cover the bridge portion of the double T only.

When the implant comprises a threaded section or other mechanicalfastening and/or retention structures, the rigidity of the augmentationmaterial may cause the required force for insertion of the implant to berather high. FIGS. 5 and 6 depict measures for reducing this force.

FIG. 5 depicts another embodiment of a device according to theinvention. The lower panel shows a cross section through the device inthe region of its distal end. The oscillation tool 3 depicted in FIG. 5comprises several laterally protruding wing structures 3.7 (or blades).These wing structures prevent the augmentation material from flowing tocertain angles and in addition may be sharpened so as to cut throughalready-hardened augmentation material as well as through bone tissue.Preferably, as in the depicted embodiment, the wing structures radiallyprotrude into the bone tissue, and axially project further to the distalside than the periphery of the liquefaction interface, so as tosustainably prevent liquefied material from flowing to the angles to bekept free from augmentation material. The effect of the wing structuresis to effectively slit the augmentation zone into different segments. Bythis, the augmented opening as a whole becomes more flexible forstretching, and a screw may be inserted more easily. Also, in weak orbrittle bone tissue, when a torque is excerpted onto an augmentationzone 6 of the kind depicted in FIG. 6, there is a risk that theaugmentation material including the trabeculae encased by it will breakloose and rotate relative to the remaining bone tissue. This risk iseffectively reduced by the splitting of the augmentation zone intounconnected segments.

A set-up as the one illustrated in FIG. 1, 2 or 5 may also be used ifthe energy coupled into the system is heat. In this case, the distalbroadening 3.2 of the tool 3 may comprise a heating element.

If the energy is radiation energy, the roles of the tool and of thecounter element are for example reversed, i.e. the counter element has adistal broadening distally of the augmentation element, and the tool,through which the radiation impinges onto the augmentation element, isproximal of the augmentation element. If the augmentation element istransparent for the used electromagnetic radiation, the radiation energyis for example coupled into the augmentation element and absorbed at theinterface to the counter element. If the augmentation element isintransparent, the energy is absorbed at the interface to the tool.

The embodiment of FIG. 6 shows an oscillation tool of which the distalbroadened portion 3.2 is formed by a rotation element that is mountedrotationally with respect to the shaft 3.1. To that end, the shaftcomprises a distal enlargement 3.8 with which the rotation element 3.2forms a swiveling positive-fit connection. Moreover, the distalbroadening comprises thread cutting portions 3.6 radially protrudingfrom the distal broadened portion 3.2. During the movement of theoscillation tool towards the proximal side, the distal broadened portion3.2 rotates about the axis and thereby cuts an inner thread in the, forexample, not yet fully hardened augmented zone 6. This, of course, alsoeases the insertion of an implant with an accordingly threaded section.

The embodiment of FIG. 7 is an example of ‘forward’ insertion of theaugmentation material: While in the above-described embodiments, atensile force was coupled into the oscillation tool, and theliquefaction interface was at a distal end of the augmentation element4, this is the other way round in the embodiment of FIG. 7. Theoscillation tool 3 is a ring sonotrode acting on the augmentationelement 4 on a proximal end surface 4.1 which thereby acts as the firstaugmentation element contact surface. The counter element 5 comprises acounter element shaft 5.3 reaching through the oscillation tool 3 andthe augmentation element 4 to a distal end of the latter, where a distalbroadening 5.2 of the counter element comprises a rearward (i.e. towardsthe proximal side) facing surface 5.1 that forms the counter elementcontact surface.

The oscillation tool contact surface 3.3 is preferably taperedoutwardly. During the augmentation process, the oscillationthermoplastic material of the augmentation element is liquefied at theinterface to the oscillation tool and is, by a pressure resulting formthe force by which the oscillation tool and the counter element arepressed against each other, displaced towards the outside and intostructures of the circumferential wall of the opening 1.1—similarly tothe above-described embodiments. The counter element 5 during thisprocess may be held still, or slowly pulled towards the proximal side.The augmentation process is continued until the oscillation tool contactsurface 3.3 and the counter element contact surface 5.1 are in contactwith each other or are at least close to each other so that the counterelement can be removed to the proximal side.

Like for all other embodiments, the structures of the counter element 5and of the (oscillation) tool 3 may optionally be adapted to each otherso that when their contact surfaces meet at the end of the augmentationprocess, they match (i.e. the shapes correspond to each other so thatthey may rest against each other by way of a surface-to-surfacecontact), or that they at least rest against each other at the peripheryso as to disrupt a connection between the augmentation material 6 andremaining thermoplastic material pulled out together with theoscillation tool 3 and the counter element 5.

While the embodiment of FIG. 7 features the disadvantage that there is alarge surface contact between the oscillating oscillation tool 3 and thebone tissue as soon as the oscillation tool is inserted deeply into theopening 1.1, this embodiment may nevertheless be suitable for certainapplications. For example, if a lot of augmentation material is to bebrought into a volume directly underneath the surface (or underneath acomparably thin corticalis), the embodiment of FIG. 7 may be suitable.Especially, the whole propulsion then may come from the counter elementwhile the oscillation tool remains immovable in its position protrudinginto the opening to a small extent only.

In all above-described embodiments, the augmentation element 4 wasassumed to be tube-shaped. While a generally tube shaped augmentationelement is advantageous because such a shape is easy to guide during theaugmentation process, is easy to handle and allows usingeasy-to-manufacture, symmetrical oscillation tools and counter elements,depending on the application also other shapes are feasible. FIG. 8 inthe upper panel schematically illustrates a cross section through anoscillation-tool 3—augmentation element 4 assembly where theaugmentation element is not circumferential but covers only certainangles. More concretely, it comprises two portions 4.11, 4.12 at lateralsides of the oscillation tool 3. The two portions may be discrete, orthey may be connected, for example, by a connecting portion at theproximal end of the augmentation element 4. The lower panel of FIG. 8illustrates a detail showing the liquefaction interface. In the depictedembodiment, the augmentation element 4.11, 4.12 is initially attached tothe oscillation tool 3, so that the two portions are fixed to the tooland to each other prior to the augmentation process. Such attaching may,for example, be achieved by pressing the augmentation element portionsagainst the oscillation tool contact surface 3.3 while either theaugmentation element portions or the oscillation tool or both are at atemperature around the melting temperature, and thereafter letting theassembly cool. During the augmentation process, the augmentation elementportions 4.11, 4.12 are held in place by the geometry of the oscillationtool and the opening in the tissue. In alternative embodiments, theaugmentation element portions instead of being attached may also beinserted after the oscillation tool has been introduced.

As a remark, the attaching of the augmentation element to theoscillation tool and/or to the counter element prior to the augmentationprocess is an option in all embodiments of the invention. Suchpre-assembly may be done during fabrication of the device, by themanufacturer, or immediately prior to the augmentation process by theuser.

The counter element used for theoscillation-tool-augmentation-element-assembly of FIG. 8 may comprisedistally protruding structures corresponding, in cross section andposition, to the structure of the augmentation element portions and,after liquefaction, interdigitating with the oscillation tool so thatthe augmentation element material may be entirely liquefied anddisplaced when the oscillation tool and the counter element abut againsteach other.

A configuration as the one shown in FIG. 8 is suitable for augmentinghard tissue and/or hard tissue replacement material that with respect tothe opening is not approximately cylindrical symmetric. An example ofsuch a hard tissue and/or hard tissue replacement material would be along bone where the opening's diameter approximately corresponds to thediameter of the trabecular portion, so that the augmentation materialwould have little room to go towards directions perpendicular to thebone axis. The bone axis would then be oriented parallel to thehorizontal in the upper panel of FIG. 8. In addition or as analternative, it is also suited for implementing the functionality of thedevice described with respect to FIG. 4, i.e. the division into aplurality of portions for different sectors (angle ranges) may also beeffective to keep sectors of the augmentation material apart and tothereby ease the introduction of a screw or the like. The cutting wings(blades) may or may not be present when embodiment of FIG. 8 is used forsuch purpose.

Whereas in the above embodiments, the in hard tissue and/or hard tissuereplacement material has been assumed to be trabecular bone tissue, theteaching equally well applies to other hard tissue and/or hard tissuereplacement material. Also, in the described embodiments, theliquefaction interface was assumed to be the interface between theoscillation tool and the augmentation element, but the skilled personknowing the present teaching can readily transfer the teaching toconfigurations where liquefaction also or exclusively takes place at theinterface to the counter element.

EXAMPLE

In a configuration as described referring to FIG. 2, with circularsymmetry with respect to the axis 2, the following device parameterswere used: oscillation tool shaft diameter 2 mm, oscillation tool distalbroadening diameter 4.4 mm, Taper inclination 45°. Tube shapedaugmentation element inner diameter 2.1 mm, outer diameter 4.2 mm.Augmentation element material: LR708. Tube shaped counter element withapproximately similar inner and outer diameters as the augmentationelement (exact sizes of the diameters not critical). The oscillationtool and the counter element were metallic, for example of stainlesssteel (material not critical).

Insertion into an opening in sawbone 12.5 PCF with an opening diametercorresponding to or slightly above 4.4 mm. A Branson E150 apparatus wasused for generating the mechanical oscillations coupled into theoscillation tool. The apparatus was operated at a frequency of 20 kHzand at a power of 105 W yielding good augmentation with a soundlyanchored augmentation zone. Also tests with operating frequencies of 30kHz were successful.

In a second example, a device with the above parameters but in additionwith blades as illustrated in FIG. 5 were used, with otherwise the sameoperation parameters.

In the more general case, for any augmentation element dimensions,Sawbone 12.5 PCF is a suitable material for testing the suitability ofthe device. The required power approximately scales with theaugmentation element cross section.

What is claimed is:
 1. A method of anchoring an implant in tissue,wherein the tissue is hard tissue, hard tissue replacement material or acombination of hard tissue and hard tissue replacement material, themethod comprising the steps of: providing an initial opening in thetissue; providing a thermoplastic augmentation element, a tool and acounter element, wherein an interface is formed between a tool contactsurface and a first augmentation element contact surface at a distal endof the augmentation element, and wherein the tool comprises a pluralityof lateral wing structures; compressing the augmentation element betweenthe tool and the counter element while the lateral wing portionsradially protrude into the tissue, while energy is coupled into thetool, into the augmentation element or into both the tool and theaugmentation element, and while a periphery of at least one liquefactioninterface is within the opening, thereby liquefying material of theaugmentation element at the at least one liquefaction interface to yieldliquefied material and causing portions of the liquefied material topenetrate into one or both of structures of the tissue and structures ofan element connected to the tissue, wherein the at least oneliquefaction interface is one or more selected from the group consistingof the interface between the tool and the augmentation element and aninterface between the counter element and the augmentation element, andwherein a force for compressing the augmentation element is coupled intothe tool as a tensile force; allowing the liquefied material to hardenand to thereby become augmentation material; removing the tool and thecounter element from the opening; and anchoring the implant, at least inpart, in the augmentation material.
 2. The method according to claim 1,wherein the tool is an oscillation tool, and wherein energy is coupledinto the tool, into the augmentation element or into both the tool andthe augmentation element by coupling mechanical oscillations into theoscillation tool.
 3. The method according to claim 1, wherein energy iscoupled into the tool, into the augmentation element or into both thetool and the augmentation element by coupling at least one of arotational movement, of heat, and of electromagnetic radiation into thetool.
 4. The method according to claim 1, wherein the opening comprisesa circumferential wall, wherein the step of compressing the augmentationelement between the tool and the counter element is carried out whilethe periphery of the liquefaction interface is adjacent thecircumferential wall, and wherein the structures into which theliquefied material is caused to penetrate are structures of thecircumferential wall.
 5. The method according to claim 1, includingmoving the at least one liquefaction interface in an axial directionwhile energy is coupled into the tool, into the augmentation element orinto both the tool and the augmentation element.
 6. The method accordingto claim 1, wherein in the step of removing the tool and the counterelement, the tool and the counter element are both removed to a proximalside.
 7. The method according to claim 1, wherein the liquefied materialafter the step of liquefying is displaced from an initial, innerposition to a final, outer position, by at least a radial distance thatcorresponds to half a wall thickness of a tube wall of the augmentationelement and is thereby caused to penetrate into the structures of thecircumferential wall.
 8. The method according to claim 7, wherein aninner diameter of the augmentation material remaining anchored in thetissue after having hardened is larger than an outer diameter of theaugmentation element before the compressing step.
 9. The methodaccording to claim 1, wherein an entire cross section of theaugmentation element is liquefied in the liquefying step.
 10. The methodaccording to claim 9, wherein the step of liquefying is carried outuntil the tool contact surface and a counter element contact surfacetouch each other.
 11. The method according to claim 1, wherein theinterface between the augmentation element and the counter element isaxially moved during the liquefying step.
 12. The method according toclaim 11, wherein the tool comprises a tool shaft and a tool distalbroadening forming the tool contact surface, and wherein the toolcontact surface is tapered with respect to the shaft to form a concavecontact surface.
 13. The method according to claim 1, wherein theimplant comprises fastening or retention structures for a mechanicalconnection and is anchored by means of the fastening or retentionstructures.
 14. The method according to claim 1, wherein the implantcomprises thermoplastic surface portions and is anchored by bonding thethermoplastic surface portions to the augmentation material.